Jeff Duquette

Lorrin Said: Regardless of barrel height, aim at target bottom with the same range setting on the gun results in the same trajectory height at the target." Absolutely right. As I said I have no argument with you on that point. But I'm throwing in the additional caveat of range estimation error and its effect on shot placement relative to barrel height and target height. It makes no difference whether we are talking about rifles or tanks. My rifle bullet example is something alot of folks here can probably better relate to. But ballistics are ballistics. The main point to remember is that – like I said – battlesight is by its very nature a shooting method that ignores range estimation and therefore will more often than not include an MPI that is offset from the point of aim as a result of the ranging error. But that is why we are trained to shoot center of visible mass. Anyway, I don’t really want to argue. Just have a look at what I’ve said and churn it around a bit in that big brain of yours. Best Regards Jeff D.

Remember that battlesight assumes no real focus on range estimation by the TC or gunner, so range errors are inherent with the technique. Now my example was not focused on battlesight per say. I am simply quantifying the effects of initial barrel height and its effect on range estimation errors. I totally agree with your previous explanation – assuming no range error is thrown into the mix. The location of the two particular trajectories in my above example do not plot right over the top of each other -- that is unless I rotate one or the others axis as well as shift the vertical axis up or down. If I rotate and do a vertical shift, than the two trajectories exactly parallel each other. But the real path to get to my aiming point is different (this concept is I suspect easy for you, but will doubtless create some confusion for a few – no offense intended to anyone). The real paths can’t be the same for obvious reasons (I’ll post something at Yahoo so you can better see what the heck I’m talking about). In my example, one trajectory starts at 6 or 8 inches above the ground, and the other starts about 60 or 70-inches above the ground, depending upon how tall you happen to be. I’m pretty tall so I’m at even more of a disadvantage. Both bullets have to get to the same aim point set at 72-inches above the ground at a range of 500-yrds. So the trajectory of my standing position bullet increases in elevation to a point and than drops back down to hit my aim point at 500-yrds. Conversely from the prone position my trajectory is rising during just about its entire flight before hitting that exact same aim point at 500-yrds. So you are right that there is no noticable effect in my zero range setting wheather I shoot from the prone or from standing. The angle is just to small to matter. But I'm speaking of the effect of a target range that is different from my zero range. Now back to battlesight – like I said at the start, let’s remember that battlesight assumes no real focus on range estimation by the TC or gunner. Thus we should conclude that range errors are a defacto part of the game. Battlesight is simply what sort of range setting I need to ensure a high first round hit probability against a surprise target. I cut my engagement time down considerably if I’m not trying to figure range. It’s a preset range used for snap shot engagements. There are a number of assumptions involved with the particular flavor of your optimum battlesight range setting. Such as; the most likely target you will encounter given the tactical situation; visibility; and the local terrain. If I'm expecting infantry and antitank guns I will likely have HE/spgr up the spout and will probably use a different preset range than if I’m expecting to encounter armor. But the effects are the same regardless. If I engage with battlesight with a preset range of 800m and my target is only at 600m (or whatever), the likely hood of hitting my target with my first round will be directly effected by the barrel height (and thus my maximum trajectory height) and the target height -- that is if we assume the gunner employs the same initial aim point in both cases -- i.e. aim center of visible mass or whatever a particular tank gunnery doctrine suggests to use for the aim point. It's simply a function of trajectory height at any given point relative to target height and initial barrel height. Obviously if the initial round sails over the target, and either the TC or gunner actually sense their tracer flying over their target they will make an elevation adjustment -- assuming they survive long enough. Think about it in terms of a guy sitting in a hull down overwatch position relative to his track mate that's not hull down.

Never mind ... looks like most of my questions have already been asked and answered. I think the only question left is what was the source of the Flak 18/36 dispersion data when firing pzgr.39? I didnt see a schusstafeln cite for this information. Is there similar data available for the 39-1?

“Lorrin Said: No, the height of the Tiger gun above the ground is not a factor as long as it doesn't become radical (like on top of a 20 story building).” I just wanted to clarify something on this thread. Lorrin is quite right in his above assessments in that there is very little effect on shot placement relative to the gun height. The angle between the line of sight and muzzle superelevation is quite tiny (that is unless the target or firer are at vastly different elevations, or the target is at extremely short range). But this all assumes that the tank commanders range estimation to his target is perfect. The significance of barrel height does come into play when range estimation errors are incorporated into the problem. So while the trajectory between a gun firing from a hull down position is basically the same in shape as the trajectory fired from level ground, the trajectory is not originating from the same height above the ground. In other words ranging errors will come into play when trying to hit a target dependent upon the height of the firer and the height of the target. Example: For the purposes of developing trajectory plots, my bullet is: (although any bullet will suffice for this example): Springfield 30-06 Norma Full Jacket (17651) Diameter = 0.308-inch Weight = 146-grains BC = 0.422-lbs/sq.-inch G1 Drag Function Muzzle Velocity = 2772-fps Standard Metro Atmospherics This example focuses upon bullet trajectory and the ability to hit a rather large target at long rifle range from either a prone or standing position even if I am not estimating my range to the target correctly. Hypothetically speaking, lets say I have a rather large piece of plywood that I am using as my target. The plywood target is say 76-inches in height. It’s just a big rectangular piece of wood that extends from ground level to 76-inches high. It's also wide enough such that any inherent lateral bullet dispersion will still strike the plywood target. Let’s also say that my aim point is 72-inches above the ground. For my range estimation error lets say my large piece of plywood is set 400-yards away from my firing position. However, I guess that the range to the target is actually 500-yards and line up my sights accordingly. I now fire from both a prone position and from standing position. The Prone Position. You will find that I will still hit the big piece of plywood if I am firing from a prone position even if I overestimate the actual range to the target. Moreover the maximum height of the bullet trajectory still passes through the "footprint" of the large plywood target. The Standing Position. If I am aiming at the exact same spot as I did from the prone position (i.e. my aim point is still a bullseye placed 72-inches above the ground on my sheet of plywood) and I have the same range estimation error, my bullet trajectory will not pass through the footprint of my sheet of plywood. The bullet actually sails over the top of my plywood by about 10 or 11-inches. Sooo…with that same 500 yard sight zero, and actual target distance of 400 yards the bullet height at 400yrds is about: prone: 74" standing: 87" My target height is 76” in height. So I’ll still schwack the plywood if I am prone, but will not hit the plywood if I am firing from a standing position. Sorry – normally I would post the trajectory plot to better demonstrate my point, but that is not so simple for this web site. If someone wants to examine the trajectory plots I will be happy to email them along.

Hi Rausch: Great research. Hopefully this puts to rest the use of pzgr39 by both the KwK-36 and Flak-18/36. And that the pzgr39 was probably being employed as early as 1942 by Flak 18/36. It’s surprising that this is even a source of debate, as this information is readily available in a number of mass produced booklets such Osprey's study of the Flak 18/36, Piekalkiewicz’s study of the 88, as well as Jentz's Panzertracts booklet on the Flak 18/36. I have several questions, but I haven’t been following the thread as closely as I should have, other than to review a couple of your last posts. Your posts caught my eye because of the extensive set of references actually being cited. You may have already answered my questions somewhere within this thread. If you have I apologize in advance for bombarding you with the questions again. The dispersion values for Flak 18/36 when firing either pzgr or pzgr-39 look very uncharacteristic for armored piercing ammunition. Typically vertical dispersion is greater than deflection, and increases at a greater rate than lateral dispersion relative to range. We are seeing quite the opposite in the values you've posted. I know that your Flak-18/36 pzgr dispersion values have been reversed in their order (i.e. the Height values have been reversed from the width values). I am assuming that either you, or the original author of this data also revered or transposed the order of the Flak-18/36 pzgr-39 values? Any thoughts on this? I want to make sure I am clear on one of your later points. The early Merkblatt for the Flak-18/36 clearly shows both the lighter pzgr round and the heavier pzgr-39 round being available at the time the manual was published (i.e. May 1942). You are indicating that pzgr-39 for Flak begins production in 1942, and that production appears to switch to Flak pzgr-39-1 in 1943. Is this correct? Do you know off hand what the 39-1 modification was? In the reference section of your post you cite a 1944 schusstafeln for the KwK-36. I am assuming this implies that the dispersion values you have quoted are for pzgr-39-1(FES) and pzgr-39-A1(FES). You also cite a 1938 schusstafeln for Flak-18/36 which presumably is the source for dispersion on the Flak 18/36 when firing the lighter pzgr round. Which of the references that you cited detail the schusstafeln for Flak-18/36 firing the heavier pzgr-39 projectile, and is their similar information available for the Flak 18/36 when firing pzgr-39-1? Thanks for yout time and consideration, and I look forward to reading your reply. Best Regards Jeff Rausch Said: Here are the values for a 50% dispersion zone. Format is distance - width x height (all in m). 8.8 cm Pzgr. fired from 8.8 cm Flak: 100 - ? x ? 500 - 0,3 x 0,2 1000 - 0,7 x 0,4 1500 - 1,1 x 0,6 2000 - 1,6 x 0,8 8.8 cm Pzgr. 39 fired from 8.8 cm Flak: 100 - 0,1 x 0,1 500 - 0,3 x 0,2 1000 - 0,5 x 0,7 1500 - 0,8 x 1,1 2000 - 1,0 x 1,6 8.8 cm Pzgr. 39 fired from 8.8 cm Kw.K. 36: 100 - 0,1 x 0,1 500 - 0,2 x 0,2 1000 - 0,2 x 0,4 1500 - 0,3 x 0,6 2000 - 0,5 x 0,9 ---SNIP---Regarding amo production I have not seen till now a detailed breakdown of the 8.8 Pzgr. 39 rounds in the subvariants. When I look on the anual ammo production summaries (which break the production numbers down to single months) I notice that the headers changed from "8,8 cm Pzgr." at the beginning, in 1942 to "8,8 cm Pzgr. u. 39" and again in 1943 to "8,8 cm Pzgr. 39 u. 39-1". This is true for the Kw.K. and the Flak production numbers, so the Flak could and did also fire the 39-1 variant. It looks to me that the 39-1 variant was introduced in 1943 while the 8.8 cm Pzgr production ceased in 1942, but the percentage of whole production was not pointed out. ---SNIP --- Sources are: 1) Geschoßblätter von Wa.Prüf. Amt 1, no date, but regarding the ammo described late 1943 or 1944. 2) H.Dv. 119/328 – Schußtafel für die 8,8 cm Kampfwagenkanone 36 (L/56) (8,8 cm Kw.K. 36), Februar 1944. 3) H.Dv. 119/763, L.Dv. 500/763 – Erdschußtafel für die 8,8 cm Flak 18 mit 8,8 cm Sprgr. L/4,5 (Kz) mit Zt.Z. S/30 oder A.Z. 23/28 und 8,8 cm Pzgr. mit Bd.Z. der 8,8 cm Pzgr, September 1938, Nachdruck von April 1940. 4) H.Dv. 481/60 – Merkblatt für die Munition der 8,8 cm Kampfwagenkanone 36, 8.1.1943. 5) H.Dv. 481/541 – Merkblatt für die Munition der 8,8 cm Flugabwehrkanone 18 (8,8 cm Flak 18) und der der 8,8 cm Flugabwehrkanone 36 (8,8 cm Flak 36), 20.5.1942. 6) L.Dv. 4402/5 – Die Munition der Flakartillerie, Beschreibung, Teil 5, Munition der 8,8 cm Flak 18, 36 und 37, Juli 1942. [ September 12, 2004, 09:00 AM: Message edited by: Jeff Duquette ]

Lorrin Said: “British evidence shows that the Tiger 88mm L56 and the Flak 88mm L56 fired different APCBC rounds at least through late 1944. Tiger used small capacity round, 88mm Flak used large capacity round.” The heavier and more accurate 8,8cm Pzgr.39 FES was employed by both the FLAK18 & 36 as well as the 8,8cm KwK36. The Flak18 & 36 were employing the more accurate round as early as 1942. The less accurate APCBC round employed by the 8,8cm Flak18 & 36 is the 8,8cm Pzgr.Patr.mBd.Z. This round was not employed by the KwK36. The 8,8cm Pzgr.Patr.mBd.Z round has a higher level of shot scatter, or a larger dispersion pattern than the FES round. Flak 18 & 36 firing pzgr 39 FES had a 50% dispersion zone at 1000m of 0,2m (horizontal) and 0,4m (vertical). Flak 18 & 36 firing Pzgr.Patr.mBd.Z had a 50% dispersion zone at 1000m of 0,4m (horizontal) and 0,7m (vertical). KwK 36 Firing pzgr 39 FES had a 50% dispersion zone at 1000m of 0,2m (horizontal) and 0,4m (vertical). The greater accuracy issue appears to be associated with ammunition type rather than the Tiger-1’s main gun being more accurate than the Flak-36. Source information: 1) H.Dv.481/541 “Merkblatt fur die Munition der 8,8 cm Flugabwehrkanone 18, und der 8,8 cm Flugabwehrkanone 36” dated May 20, 1942. 2) H.Dv.481/60 “Merkblatt fur die Munition der 8,8 cm Kampfwagenkanone 36”, dated Jan 1, 1943.

While it’s always a bit awkward to try and extrapolate modern tank crew training with WWII-era applications, it is never the less sometimes tempting to look at such things. I won’t play up my experience, as it was limited to training with a National Guard armor unit for six years. We would typically shoot our tank tables twice a year at Ft. Irwin. There – that’s my brief practical experience resume. Take the rest of this for what it is worth. From my own experience, there was never an occasion in which range or fall of shot were being assessed by anyone other than the TC and gunner. And the vast majority of this sort of thing was the responsibility of the TC. He made the calls on what targets to engage, what ammunition to use and what range settings to employ for an engagement. The TC also was the guy that made macro-range change commands based upon his observations of the fall of shot. The gunner was expected to automatically make micro-changes in deflection and elevation based upon his own observation of fall of shot – “placing burst on target”. He does this automatically as obviously the TC cannot know what the gunner’s exact site picture is during an engagement. So the TC calls out macro adjustments in range and deflection; on the other hand micro-adjustments – BOT – are automatically done by the gunner. That is how I was trained by Regular Army dudes at Ft Irwin. I was trained as a driver, loader and gunner and played around as a TC – but never played as TC on the gunnery range. As a loader, I never felt I had the time to be peeping out of my hatch or through a periscope to watch fall of shot. Nor was I expected to be doing this sort of thing. And it would have been rather irregular from me to be attempting to do such a thing and subsequently butting into the normal sequence of gunnery commands and alerts. I was to busy humping ammunition as quickly as I could from ready racks. That was about all I could do when we were shooting an engagement at a rate of about 1-round every 7 to 10 seconds. As a driver on a gunnery range, we were always buttoned-up. You could peer through your various vision periscopes but you cant really see much other than what’s immediately out in front of your tank. Picking up the fall of shot at 1000- to 2000 yards was not practically possible. You are trained to shoot fast and accurately or your told by your trainers that you will be dead. There wasn’t the time and there certainly wasn’t a training mechanism in place to reinforce any notation of a TC asking each of the crewmen what they thought the range was. The speed of the engagement didn’t allow for such things. I suppose if I heard this sort of question crackling in my tank intercom, I would wonder to myself “does this TC really know what the heck he is doing”? Being the TC is to a fair extent about cocky assuredness in your own abilities. The guy has to exude a fair amount of confidence. It's important to the crew to feel that the guy in charge of their tank knows what he is doing at all times. So the idea that the TC would be asking his crew for their opinion on range just seems very odd to my understanding of the way tank crews work. But this is all just my opinion and certainly not based upon sitting in a Tiger Tank during WWII. Perhaps panzer-crews did this sort of thing. Personally I would have a look at standard fire commands used by panzer crews. Do these suggest crew wide participation in the ranging process? From what I’ve seen panzer crew firing commands are very similar modern US Army firing commands.

Thanks Rupert.

So does anyone know where I can download scenarios for any of the tank battles associated wth: Brevity Battleaxe Or Crusader Thnx

I haven’t posted here in many moons but felt compelled to pop in for a quick complement. I finally decided to order a copy of Combat Mission Afrika Korps. I ordered it late Friday (that was Friday Jun 11) after getting an email from a bud saying he was interested in doing some PBEM. The game was in my mail box this afternoon! That’s like only one working day between placing the order and getting the game. How is this possible? I have no idea where Battlefront Games is located relative to me – but I’m beginning to wonder if they are working out of the basement in the house across the street. Thanks for the lightening fast order process and delivery. And thanks to USPS. I'd also like to thank the Acadamy... Best Regards Jeff Duquette

Both vehicles used the 90mm M3 Gun. There were two iterations of 90mm M82 APC ammunition produced. The early version had a muzzle velocity of 2650-fps (807.72 meters/second). The late war souped-up version had a muzzle velocity of 2800-fps (853.44 meters/second). Apparently many of the early production run versions of the M-36 were not outfitted with muzzle breaks and couldn't (or wouldn't) be retro-fitted with such due to the additional requirements of installing a more robust equilibrator, elevating mechanism and heavier travel lock. I would surmise that the earlier versions of the M36 and its lack of muzzle break made it incapable of handling the recoil shock associated with the souped-up version of 90mm M82 APC.

Lorrin Said: “Using the available data the following vertical penetration figures were generated:” You say BR-350P – from trials -- perforates a Tiger-1 frontally at 100m. None of the Tiger-1’s frontal hull plates are vertical. Assuming we are talking about the upper hull plate, I would presume that 102mm penetration by BR-350P at 100m implies performance against a ~9-degree inclination.

A URL for some very nice material for any folks working on Canadian Armor MODs: http://www.armouredacorn.com/Reference/CVM/Default.htm

It should just be Spaced plate erosion by determine the t/d ; angle & effectiveness of the plate material . Then (t/d)^0.5 to determine the 'spaced plate effect' So 2cm Aluminum [0.5d] vs 3cm API becomes 2/3÷2^2=0.8 x 2= 1.6 1.6 x 0.5[te]= 0.8cm The spaced plate effect becomes 0.8/3^0.5 = 0.5cm If there is insufficent gap, multiply 'spaced plate effect'by x 0.7. If the penetrator is high strength reduce the 'spaced plate effect' by x 0.7 So if the penetrator was high strength and the gap insufficent it should be x 0.5. </font>

Greg: I have actually been out of town for work for the last week. Down on the Oregon coast -- east of bum-fu#%ed Egypt -- working on a revetment wall. I am accessing the net via a painfully slow phone modem. My regular home email my be overflowing. I should be home tommorrow and will clear everything out.

Paul Said So 2cm Aluminum [0.5d] vs 3cm API becomes 2/3÷2^2=0.8 x 2= 1.6 Is that supposed to be (2/3/2)^0.2

I’m not sure I get it. You are now saying the velocity component is not included in the spaced effect modifier? So the spaced effect, or spaced modifier is not: (t/d)^0.5 x 0.1d x V{in Km/s} x gap modifier ???

Paul: The trend is about the same with 57mm AP. The firing trial results against the spaced armor arrays seem to indicate an equivalent single plate being lower than what the equation you have presented would predict. Of particular interest is 57mm AP and APC trials that seemingly show a lower equivalent armor thickness for the parallel plate arrangement…---->/ /. This trend doesn’t seem to hold true with the 90mm APC round. In all but one case, both the spaced armor arrays …---->/ /…and …---->/ \ were typically resulting in higher BLs than the single plate -->/. Does the equivalent spaced armor equation you have presented have its origins in long-rod penetrator firing trials? ================================================== 57mm AP M70 Results Armor Arrangement 1: 57mm AP M70 vs. 2” plate at 40-degrees ---->/ Firing Trials Ballistic Limit (BL) = 1997-fps => 1997-fps for t/d of 0.89 and AP vs RHA at 40-degrees does equate to typical BL for 2” worth of protection. Checks out. ============================================== Armor Arrangement 2: 57mm AP M70 vs. ½” Skirt Armor 16-inches away from a 2” main plate. Both plates are sloped at 40-degrees and are parallel to each other. ---->/ / Firing Trials Ballistic Limit (BL) = 1772-fps => 1772-fps at 40-degrees equates to an equivalent single plate of about 1.95”. So the firing trials indicate that this particular spaced armor array is actually less efficient than a single 2” plate inclined at 40-deg. Your equation predicts an equivalent armor thickness of ~3.32” Skirt Armor Plate Equivalent = 0.4204” Main Armor Plate Equivalent = 2.219” Spaced Armor Modifier = +0.682” (at a striking Velocity of 1772-fps or ~0.5401Km/s) 0.4204” + 2.219” + 0.682” = 3.32” ================================================= Armor Arrangement 3: 57mm AP M70 vs. ½” Skirt Armor 16-inches away from a 2” main plate. Both plates are sloped at 40-degrees and inclined in opposite directions. ---->/ \ Firing Trials Ballistic Limit (BL) = 2620-fps => 2620-fps at 40-degrees equates to an equivalent single plate of about 2.7”. So the firing trials indicate that this particular spaced armor array is actually somewhat more efficient than a sstraight-up 2” + ½” plates inclined at 40-deg. Your equation predicts an equivalent armor thickness of ~3.65” Skirt Armor Plate Equivalent = 0.4204” Main Armor Plate Equivalent = 2.219” Spaced Armor Modifier = +1.008” (at a striking Velocity of 2775-fps or ~0.845Km/s) 0.4204” + 2.219” + 1.008” = 3.65” [ November 18, 2003, 11:04 PM: Message edited by: Jeff Duquette ]

Paul: I compared the results of the equations you laid out within this thread with the APG Spaced Armor Report (Nov 1950). The results are of some interest. A little background; The APG Report details three different test armor plate arrangements. The first arrangement is simply a plate at some obliquity. Like so: ---->/ (slashes being the plate or plates and arrow the projectile) The second arrangement –spaced armor arrangement A -- was a spaced armor arrangement, with the skirting plate and main armor plate set 16” apart. The plates are parallel to each other and sloped, like so: ---->/ / The last arrangement –spaced armor arrangement B -- is as above except the plates slope in opposite directions, like so: ---->/ \ Four different projectile types were employed within the tests, to include: 57mm APC M86 57mm AP M70 90mm HVAP M304 90mm APC T50E1 =============================================== 57mm APC M86 Comparing your equations with the firing trial results for Armor Arrangement 1: 57mm APC M86 vs. 2” plate at 40-degrees ---->/ Firing Trials Ballistic Limit (BL) = 2149-fps => 2149-fps for t/d of 0.89 for APC vs RHA at 40-degrees actually does equate to 2” worth of protection. Checks out. ================================================= Armor Arrangement 2: 57mm APC M86 vs. ½” Skirt Armor 16-inches away from a 2” main plate. Both plates are sloped at 40-degrees and are parallel to each other. ---->/ / Firing Trials Ballistic Limit (BL) = 1943-fps => 1943-fps at 40-degrees equates to an equivalent single plate of about 1.91”. So the firing trials indicate that this particular spaced armor array is actually less efficient than a single 2” plate inclined at 40-deg. Your equation predicts an equivalent armor thickness of about ~3.39” Skirt Armor Plate Equivalent = 0.4204” Main Armor Plate Equivalent = 2.219” Spaced Armor Modifier = +0.747” (at a striking Velocity of 1943-fps or ~0.592Km/s) 0.4204” + 2.219” + 0.747” = 3.39” ================================================= Armor Arrangement 3: 57mm APC M86 vs. ½” Skirt Armor 16-inches away from a 2” main plate. Both plates are sloped at 40-degrees and inclined in opposite directions. ---->/ \ Firing Trials Ballistic Limit (BL) = 2755-fps => 2755-fps 40-degrees equates to an equivalent single plate of about 2.86”. So the firing trials indicate that this particular spaced armor array is actually somewhat more efficient than a single 2” + ½” plate inclined at 40-deg. Your equation predicts an equivalent armor thickness of about ~3.71” Skirt Armor Plate Equivalent = 0.4204” Main Armor Plate Equivalent = 2.219” Spaced Armor Modifier = +1.068” (at a striking Velocity of 2775-fps or ~0.845Km/s) 0.4204” + 2.219” + 1.068” = 3.71”

Thanks Paul.

Thanks Paul. Sorry to be a chuckle-head but I have several more areas of clarification...if you would be kind enough to continue to indulge me Paul Said: For example 37mm Vs 45mm SHS of T-34 glacis is [45mm/37mm/2 ^0.2]*1.2 or 49mm @ 60°...while if 75mm hits thats [45mm/75mm/2 ^0.2]*1.2 or 42mm @ 60°. How are you accounting for the angle of attack? Should “Te” be 49mm/COS(60) And 42mm/COS(60) for the 75mm dia projectile attack example? ================================= I am assuming the 1.2 multiplier is a function of the homogeneous hard armor on the T34? The RHA multiplier being 1.0; FHA multiplier is 1.3; and SHS multiplier is 1.2. Is this correct? ================================== In one of your earlier posts you indicated: So 3cm FH @ 10° t/d should become (3cm/7.6cm/2)^0.2 x 1.3[Te FH] => 0.723 x 3cm x 1.3 = 2.82cm @ 10°= 2.9cm This looks to me like you divided the resultant 2.82cm by COS(10-deg) to get the final thickness of 2.9cm…although I am getting 2.86cm after dividing by COS(10). You rounded up? Was this in fact what you were doing? In addition the 50cm Stug-111 plate…shouldn’t the final thickness or “Te” be modified by its angle of inclination as well? 52cm/COS(10)???

Paul: I have a couple of additional questions I am hoping you can wade through. After looking at your write-up a bit closer I realized you are not saying the minimum air-gap would have to be 1.77cm. 1) What -- if any -- modifications would occur to the spaced armor modification if the plates were some other steel combination…say RHA skirt over RHA main armor instead of the FH over FH which is being considered in this example? 2) Why is the air-gap advantage applied to the thickness of the skirting plate? Why isn’t the thickness of the main plate employed in determining the spaced armor added advantage? 3) You have specified an optimal air-gap space of >1d. Is there any added advantage if the air-gap is say 1.5d or 2d or 3d. The way in which you have presented your equation, the spaced armor advantage is purely a function of: The skirting plate thickness; Projectile diameter; and Projectile striking velocity. Is there no added advanatge for an air gap wider than 1d? 4) Along the same lines as Question 3 except in the opposite direction. You have indicated that anything less than about 1d would fall into the range of less than optimum spacing. However you have really not established a lower bound. Is there a point at which no real spaced armor effect would occur. Are we talking 0.1d or 0.5d; or will an air gap equal to the width of an oxygen molecule be sufficient to rate a spaced armor advantage? ;o) Regarding the 90mm HVAP example cited, the warping resulted in a 2-inch airgap. This is about equal to the diameter of the M304's penetrator. 5) Just to clarify in my own mind…your final assessment of the Stug-III armor you indicated: 2.9cm + 2cm (air gap) + 5.2cm = 8.1cm => 10cm The 5.2cm is derived from: ((5cm/7.62cm/2)^0.2)*5cm*1.3….is this correct. Thnx [ November 17, 2003, 06:40 PM: Message edited by: Jeff Duquette ]

Paul: Thanks for the in-depth explanation. And even more thanks for working through an example problem. What is the “Te” abbreviation? I would tend to agree with Lorrin on allowable plate camber for the PzIIIH example; particularly over the short span between hard connections that we are talking about with the PzIIIH's bolted on frontal armor. 1.77cm seems like a fairly large non-spec air gap over a span of what?...1 or 2 feet between bolt lines? Even if the exterior plate and interior plates were conected with concavity in opposite directions. This does however bring the whole question of implied value of additional track blocks...again. The lower front plate of most PzIII’s typically will have an extra length of track draped over it. Not that this has anything to do with the rather rudimentary firing trial data presented in the Cario Tests. However, in actual combat I can easily imagine a 1 or 2 inch air gap existing between the track blocks and main armor.

Paul said: The Stug-IIIF are produced with 30mmFH + 50mm FH armor which resists like 2.6+ 4.8cm or 7.4. However these were bolted and if there is any airgap developed between [warping] the plates that should shatter the projectile. The result is + 0.24d or 1.9cm additional resistance to a total of 9.3cm RHAe, which limits T-34 76mm AP shell to ~0-900m penetration [½ hits], depending on if theres an airgap or not. The Stug-IIIf own 75L46 gun penetrates T-34 at….. This is pretty divergent from your post about a year back on the Yahoo Tankers Forum. I had brought up the air-gap being of some significance on the KV-1E’s bolted on armor. You indicated that this small air gap would have little or no effect on normal AP if the dimension of the air gap was not at least as large as the diameter of the projectile. You than went on to say that these smaller air-gaps might affect the performance of HVAP\APCR. Is there some reason why you are now changing your opinion on this particular aspect of terminal ballistics? Bear in mind we are not talking about analogies to long slender APFSDS. These are big fat, blunt projectiles that would be striking a STUG-III’s armor. [ November 16, 2003, 11:38 AM: Message edited by: Jeff Duquette ]

The two actions described above are detailed in the following write-ups. From Volume IV of the Anti-Armor Defense Data Study by Michael Bailey & Lloyd Karamales (et al.): [ACTION 1] As soon as the barrage lifted, the men of B Co were startled to see an American jeep, driven by Germans, approaching them up the hill from Losheim. The jeep halted before It reached the American line, literally under the nose of one of the 57mm AT guns which was hidden about 50 meters north of the road on the south slope of Hill 666. In the diffused glare of the spotlights which the Germans behind the Westwall were bouncing off the low clouds, the gun crew could clearly see the jeep and its occupants, but in their surprise and uncertainty they hesitated to fire. Turning around, the jeep sped off back down the slope and into Losheim. A few minutes later it reappeared, leading what some accounts say was a tank. However, since the 12th Volksgrenadier Division had no tanks attached to it, the vehicle was instead almost certainly a sturmgeschutz (StuG III 75mm self-propelled assault gun) belonging to the division's organic 1012th StuG Co. Postwar accounts by the commander of the 48th Gren Regt, Col Wilhelm Osterhold, confirm this supposition, and mention that German infantry were riding on the sturmgeschutz. The American AT gun crew again let the jeep pass, but fired on the assault gun as it drew up in front of their gun. The first round struck the vehicle in the right flank, knocking off a track and immobilizing it. The second and third shots penetrated the vehicle's starboard hull, with the third shot setting the assault gun aflame. Some accounts say the only survivor of the crew was the commander, a lieutenant, who was badly wounded and who staggered from the wreck. Others say the entire crew bailed out, apparently unhurt, and began firing small arms at the AT gun crew. Considering the scarcity of flank armor on the StuG III and the proximity of the AT gun when it fired, the former outcome seems far more likely. The infantrymen of B Co, farther up the road toward Losheimergraben, killed the occupants of the captured jeep with small arms fire at the same time as the assault gun was destroyed. =================================== [ACTION 29] Farther to the southwest, at the CP of Col Barsanti's 3/38th Infantry, Maj Vivian Paul, the 38th Infantry Regiment's S-4, was just leaving to return to the Regimental CP in Rocherath after a meeting with Col Barsanti. He and his driver had just gotten into their jeep, parked in front of the CP, when the surviving Panther "rounded the corner going lickety-split," headed right for them. Maj Paul and the driver leapt from the jeep and rolled into a roadside ditch just as the Panther slammed into the jeep and crushed it. At that moment, one of the 57mm AT guns of the 3/38th's AT Platoon, which was covering the Route vers Udenbreth against just such a German incursion, fired at the Panther. The shell struck the panzer and apparently damaged the turret traverse mechanism, for the Panther continued down the street but "with the turret swinging wildly, completely out of control." [ACTION 29] The 3/38th's Assistant S-3, Lt Fred Sutton, was nearby and had witnessed the whole episode. He ran to a nearby Sherman tank and notified them of the Panther in the neighborhood. The Sherman quickly fired a round at the Panther but missed. The Panther was lost to the Sherman's view before the American tank could fire a second shot. The Panther pressed on toward Bollingen, approaching the L Co CP. Just as it passed in front of that building, a self-propelled TD from the 644th TD Bn, which Col Barsanti had placed near the 3/38th CP to guard against a German attack from BoIIingen, fired three rounds in rapid succession into the Panther's thinner rear armor at a range of 250-300 yards. That finally stopped the rampaging Panther, and as the crew bailed out of the tank, the L Co riflemen picked them off. When the panzer's hulk was examined later, it was found to have II bazooka holes in it (none of which apparently penetrated all the way through the armor), as well as the three TD penetrations in the rear and whatever mark the AT gun's round had left. ================================================== I uploaded a scan from Vol IV of the Anti-Armor Defense Data Study, Action 29. The study breaks down all Action details in the same manner. Copy and past the following URL into your browser address box – hit enter to view. http://www.geocities.com/tigervib_2000/Action29.jpg Of particular interest is the box toward the end of the chart that breaks out typical ammunition load out. There is no mention of 57mm SABOT being a "normal" ammunition type for this weapon. [ June 24, 2003, 09:47 AM: Message edited by: Jeff Duquette ]